1. Field of the Invention
This invention relates to a liquid crystal display wrist watch having an improved construction adjacent to a display part and particularly having an improved support and the like for a liquid crystal display cell.
2. Description of the Prior Art
Generally a liquid crystal display device has mounted to thereon, a display panel, which includes a liquid crystal cell composed of a pair of glass plates, a liquid crystal film sandwiched between these glass plates, and a transparent electrode and reflecting electrode vapor deposited on each of the glass plates.
Depending on the type of liquid crystal, the liquid crystal cell may further include a polarizing plate and a reflecting plate.
The liquid crystal cell is mounted on the display device by holding the glass plate constituting the liquid crystal cell. It is difficult to precisely work the glass plate so that difficulties arise in precisely mounting the liquid crystal cell on a timepiece or the like, wherein it is required to mount the liquid crystal cell thereon by taking the mounting precision into consideration.
In addition, a liquid crystal cell applied to electronic timepieces so as to display times must be supported at a position which is correct with respect to a timepiece substrate on which are mounted a step-up circuit and other circuits. Moreover, connection terminals corresponding to a number of segments constituting a display surface must reliably be connected to connection terminals of an electronic circuit.
In general, the display by the liquid crystal cell is effected by a difference in contrast between the substrate and the display patterns produced by external light projected thereon. In a liquid crystal display element which makes use of a polarizing plate such as, for example, a twist liquid crystal and the like in which rotary effect of a polarizing surface of a liquid crystal layer is controlled by an electric field, the substrate is preferably made of a material having a high reflective as much index for the purpose of reflecting light from the substrate as possible.
Heretofore, with a reflection type display element which makes use of a polarizing plate of the twist liquid crystal, type it has been the common practice to use a rear reflecting plate made of an aluminum foil. In this case, the total surface of both the polarizing plate and the reflecting plate are adhered to glass plates with the twist liquid crystal sandwiched therebetween with the aid of a transparent adhesive agent. Alternatively, in the liquid crystal timepieces, the polarizing plate, reflecting plate and glass plates are incorporated into and secured to the timepiece by means of screws and the like.
If the reflecting plate is adhered over its total surface to the glass plates, bubbles are occluded in the adhesive layer during the manufacturing step and, hence, results in a material decrease in yield and the disadvantage that it is difficult to determine the correct relative position between the glass plate and the reflecting plate. If use is made of a reflecting plate with characters, patterns and the like printed thereon, difficult problems arise that the adhesive agent causes a blur of the printing ink and the like.
In addition, the liquid crystal cell for supporting the display part of the liquid crystal display wrist watch inclusive of an electrical connection between the liquid crystal cell and output terminals of a liquid crystal driving circuit must be mounted carefully on the wrist watch substrate. That is, the electrical connection between the terminals of the liquid crystal cell and the output terminals of the liquid crystal driving electronic circuit is reliably held in a stable manner and the liquid crystal cell with the liquid crystal sandwiched between two flat plates made of inorganic material such as glass the like is so held on the wrist watch substrate that no cracks occur in the glass.
Heretofore, it has been the common practice to adhere the liquid crystal cell to the circuit substrate by means of an conductive paste or the like or to support the liquid crystal cell by a metal plate or to adhere the liquid crystal cell to a member such as a boundary plate or the like.
It is a matter of course that a wrist watch movement which is thin, and which can display various kinds of functions and the like will be developed in future. For this purpose, the liquid crystal cell must be thin or the display area must be enlarged. In such a case, it is inevitable with the prior art technique that difficult problems arise in that the above described electrical connection is not reliable or the liquid crystal cell becomes broken by slight shocks.
In addition, indium oxide or tin oxide is suitable for the electrode of the liquid crystal cell provided for the liquid crystal display device. In view of its chemical properties, indium oxide is preferable and hence the electrode of the liquid crystal cell is often made of indium oxide.
Exterior electrodes of the liquid crystal cell may also be made of indium oxide. But, due to its chemical properties indium oxide per se is not preferable as a contact metal. Preferably, output terminals of the liquid crystal driving circuit may be made of a metal selected from the group consisting of gold, platinum, silver and paradium. These metals are suitable from their chemical property as the contact metal.
The standard oxidation electric potential E.degree. of indium oxide is 0.342 V, that of gold is -1.50 V, that of platinum is about -1.2 V, that of silver is -0.800 V and that of paradium is -0.987 V. As a result, no high oxidation electric potential difference occurs at the contact point between the exterior electrodes and the output terminals and hence the contact point is not corroded.
A liquid crystal display cell used, particularly, for a wrist watch and the like on which are arranged a plurality of very small digital characters, symbols and the like, must usually be provided with 10 small connection terminals.
As described above, the liquid crystal cell of the liquid crystal display device is composed of two glass plates, two electrodes deposited on the opposed surfaces of these glass plates and a liquid crystal sandwiched between the electrodes. It is effectively useful to expose terminals of these electrodes at the exterior of the liquid crystal cell by taking into consideration the connecting condition between these electrodes and the output terminals of an integrated circuit for delivering electric signals to a liquid crystal display pattern or the mounting condition of the liquid crystal cell on the substrate of the display device.
If use is made of a metal supporting member for mounting the liquid crystal cell on the display device substrate, there is a risk of the electrode terminals being shortcircuited by the metal supporting member.
In addition, in the twist type liquid crystal whose optical axis is rotated by 90.degree. by the electrical field applied thereto, provision must be made for a polarizing plate and a reflecting plate for the purpose of improving contrast in the liquid crystal display. In this type of twist liquid crystal display device, heretofore, it has been the common practice to make the polarizing plate and reflecting plate equal in size to the glass plates. As a result, in case of incorporating the liquid crystal cell into the display device, metal fixtures are urged upon the polarizing plate so that that part of the polarizing plate which is covered by the metal fixture becomes useless. As a result, if the twist type liquid crystal is used in wrist watches, for example, whose size must be made small, the above described construction, which does not use available space, is not suitable.
In addition, the use of an adhesive agent by which the polarizing plate and reflecting plate are adhered to the glass plates results in the disadvantage of the adhesive agent protruding from the peripheral edges of the glass plates.
In general, a liquid crystal display timepiece preferably utilizes an oscillator and particularly a high precision crystal oscillator. Such crystal oscillation type timepieces have a high frequency and comprise an oscillator circuit, a frequency dividing IC circuit, a display decoder circuit, an electric source battery, an exterior control device and or the like. These devices have the disadvantage that it is difficult to provide a crystal oscillation type timepiece which is sufficiently thin in thickness and small in size if compared with the customary mechanical type timepiece. In addition, the size is increased by adding various kinds of devices, such as for example, an alarm device, a stop watch and chronograph is added to the crystal oscillation type timepiece. If the liquid crystal display cell, which is the largest among the constitutional elements of the timepiece except for its outer case, can be made small in size and thin, it is significantly beneficial to make the wrist watch small in size and, particularly to make the wrist watch thin. Moreover, the liquid crystal display cell must be replaceable by new one so that it must be strong, light in weight and thin in thickness.
As described above, when mounting the liquid crystal cell on the timepiece substrate, the connection between the exterior electrodes of the liquid crystal cell and the output terminals of the liquid crystal display driving circuit is effected. But, there is a risk of the connection between the exterior electrodes and the output terminals slipping after the liquid crystal cell has been mounted on the timepiece substrate. In addition, if the liquid crystal display ceases its normal operation, the liquid crystal cell must be removed from the timepiece in order to ascertain its fault. Moreover, an increase in number of displays such as hours, minutes, seconds, dates, week days and the like results in an increase in number of the exterior electrodes of the liquid crystal cell, and as a result, the above described disadvantage due to the slip of connection between the exterior electrodes and the output terminals becomes conspicuous.
In designing or manufacturing a liquid crystal display timepiece, heretofore, it has been well known that the life of the liquid crystal per se is far shorter than the life, reliability and the like of the electronic circuit and the like for driving the liquid crystal. As a result, a need arises to easily replace the liquid crystal cell with a new one. Thus, a number of liquid crystal display timepieces, in which the liquid crystal cell can be replaced by a new one, have been proposed. But, most of these liquid crystal display timepieces have encountered a difficult problem in that the replacement of the liquid crystal cell by a new one becomes troublesome as the electrical connection between the exterior electrodes and the output terminals of the electronic circuit must reliably be effected. For example, the liquid crystal cell could not be removed from the timepiece substrate unless all of screws are loosened and removed from the metal fixtures for securing the liquid crystal cell to the timepiece substrate.
Needle type wrist watches have recently been intended to follow the latest fashions and become colorful. It is also desirous that the liquid crystal display wrist watches follow the latest fashions and become colorful. Particularly, it is desirous to provide many varieties of boundary plates for the liquid crystal wrist watch, as is the case with many varieties of dial plates for the needle type wrist watch. But, the conventional boundary plate is composed of a mask printed on the lower surface of a protective glass cover or is made integral with the liquid crystal cell so that the conventional boundary plate could not be separated from the liquid crystal cell, and as a result, it is difficult to provide many varieties of boundary plates for the liquid crystal display wrist watches.
In addition, it has also been proposed to use voltage so as to change the color of the liquid crystal. But, such means is not used in practice. It is also possible to change the color of the liquid crystal of the twist type liquid crystal display timepiece by selecting the color of the upper and lower polarizing plates. But, such colored polarizing plates must be manufactured in a manner which is easier than the method of manufacturing the dial plate and must have a polarizing property. As a result, the kinds of polarizing plate which are usable for colored polarizing plates are limited in number. In addition, the polarizing plate is secured to the glass plate by means of the adhesive agent so that a selection of the color of the upper and lower polarizing plates results in a need to alter the display device as a whole. As a result, the kinds of polarizing plates which are usable as the colored polarizing plate, are also limited in number.